Liquid bleaching compositions are well-known in the art. Amongst the different bleaching compositions available, those relying on bleaching by hypochlorite are often preferred, mainly for performance reasons, especially at lower temperature.
However, there are some limitations to the convenience of hypochlorite bleaches. In particular, it is well-known from consumers that the drawbacks associated with the use of hypochlorite-based compositions are that said compositions may damage and/or yellow the fabrics which are being bleached.
It is therefore an object of the present invention to provide a hypochlorite-containing composition, suitable for use in laundry application, whereby the fabric whiteness is improved.
It is a further object of the present invention to provide a hypochlorite-containing composition, suitable for use in laundry application, whereby fabric safety is improved.
We have now found that the previous objects can be met by formulating an alkaline liquid composition comprising an alkali metal hypochlorite or mixtures thereof and a pH buffering means with low sensitivity to water hardness, i.e. a pH buffering means which, when used in a 1M solution at pH 10, requires more than 2.5 mM of calcium ion, in order to cause precipitation at 25.degree. C. of the calcium salt of the alkali anion of said pH buffering means. Said composition allows to provide improved fabric whiteness and/or improved fabric safety on the fabrics treated therewith, as compared to the same composition without said pH buffering means with low sensitivity to water hardness according to the present invention. We have also found that, in the preferred embodiment of the present invention wherein the liquid hypochlorite bleach-containing compositions comprise said pH buffering means with low sensitivity to water hardness together with a precipitation agent like carbonate salt and/or silicate salt, outstanding whiteness and/or fabric safety performance are provided. Indeed, it has been found that the use of a pH buffering means with low sensitivity to water hardness together with a precipitation agent like silicate salt and/or carbonate salt in a hypochlorite bleaching composition results in a complementary effect on fabric whiteness performance and/or fabric safety performance.
An advantage of the compositions of the present invention is that they allow to provide outstanding fabric whitening action and/or fabric safety properties without compromising on the stain removal performance on different types of stains including bleachable stains (e.g. coffee), enzymatic stains (e.g. blood) and greasy stains (e.g. lipstick).
Another advantage of the compositions of the present invention is that said bleaching compositions are suitable for the bleaching of different types of fabrics including natural fabrics, (e.g., fabrics made of cotton, viscose, linen, silk and wool), synthetic fabrics such as those made of polymeric fibers of synthetic origin as well as those made of both natural and synthetic fibers. Indeed, the compositions of the present invention may be used on synthetic fibers despite a standing prejudice against using hypochlorite bleaches on synthetic fibers, as evidenced by warnings on labels of commercially available hypochlorite bleaches and clothes.
A further advantage is that the liquid compositions according to the present invention comprising a pH buffering means with low sensitivity to water hardness allow a prolonged through-the-bleach buffering action, i.e. to maintain the pH of the bleaching solution as high as possible during the whole bleaching cycle from the moment the dilution is completed, without increasing the pH of the compositions per se as compared to the same compositions but without said pH buffering means.
Compositions comprising hypochlorite and pH buffering means have been described in the art.
WO 88/05462 discloses a composition for removing stains from fabrics comprising an aqueous solution of trisodium phosphate, sodium hydroxide, sodium hypochlorite and a buffer to maintain a pH of between about 10 and 12 such a sodium carbonate, sodium bicarbonate, sodium sesquicarbonate or mixtures thereof. WO 88/05462 further discloses that it is preferred that the buffer system employed holds the pH as close to pH 10 as possible, consistent with effective stain removal to provide a product which is more gentle to skin and fabrics than a higher pH. WO 88/0562 also discloses a process of removing stains from fabrics with said compositions. However, pH buffering means having a low sensitivity to water hardness as described herein are nowhere disclosed in WO 88/05462.
EP-A-622 451 discloses compositions suitable for use in diluted form, comprising hypochlorite, sodium hydroxide, a bleach stable perfume and as a buffering system whereby the pH of the diluted composition is buffered to a constant value throughout use, carbonate and/or silicate. EP-A-622 451 also discloses a method of bleaching wherein such a composition is contacted with fabrics. No pH buffering means with low sensitivity to water hardness are disclosed.
EP-A-653 482 and EP-A-668 345 disclose hypochlorite-containing compositions comprising a source of strong alkalinity, a pH buffering means and optionally other types of ingredients such as respectively radical scavengers and polycarboxylate acids of pyridine. The pH buffering means disclosed therein are alkali metal silicate and/or carbonate, sodium borate and sodium sesquicarbonate. pH buffering means having a low sensitivity to water hardness as described herein are nowhere disclosed in said patent applications.
UK 1282 906 discloses stabilised aqueous alkali metal hypochlorite solutions comprising as a stabiliser an alkali metal heptonate or boroheptonate. "Alkali metal boroheptonate" as used in UK 1282 906 refers to a mixture of an alkali metal heptonate with either boric acid or an alkali metal metaborate and generally containing two gram moles of alkali metal heptonate per gram atom of boron in the boric acid or metaborate. However, no strong source of alkalinity nor the pH of the solutions therein are disclosed. Also no laundry application is disclosed.
BE-749728 discloses an aqueous system comprising an N-hydrogenate and a hypohalite such as hypobromite, hypochlorite or hypoiodite in equilibrium with the corresponding N-halogenated compound, and a buffering system to maintain the pH of said system in a range of 4 to 11 to stabilise it before use. The buffering system mentioned therein are generically acetates, carbonates, phosphates, polyphosphates, organophosphates, borates, polyborates, organoborates, silicates, polysilicates, organosilicates or mixtures thereof. Strong sources of alkalinity such as sodium/potassium hydroxide are also disclosed. These bleaching compositions are particularly suitable to bleach textiles. But BE 749728 fails to make a distinction between pH buffering means being sensitive to water hardness like silicates or carbonates and pH buffering means with a low sensitivity to water hardness, as the ones described in the present invention.
U.S. Pat. No. 4,000,082 discloses defoaming compositions based on lithium salts. More particularly, U.S. Pat. No. 4,000,082 discloses aqueous cleaning compositions comprising anionic surfactants, nonionic surfactants, from 5% to 50% by weight of the total composition of a highly alkaline compound selected from the group of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium metaborate and the like, and from 1% to 5% by weight of a lithium salt including lithium hypochlorite. No bleaching application is disclosed, let alone laundry bleaching application.
Actually, the benefits derivable from the use of a pH buffering means according to the present invention, which, when used in a 1M solution at pH 10, requires more than 2.5 mM of calcium ions, in order to cause precipitation at 25.degree. C. of the calcium salt of the alkali anion of said pH buffering means, in an alkaline liquid bleaching composition comprising hypochlorite, for bleaching fabrics, i.e. improved fabric whiteness and/or fabric safety on the fabrics treated therewith, have not been acknowledged in the prior art.